MFE 659 Lecture 1a Intro

Transcription

1 MFE 659 Lecture 1a Intro FORECASTING A brief intro to this block My specialty - high impact weather Scientific method - forecasting Global Winds and the Jet Stream Text Weather Forecasting as an iterative process is a prime example of the scientific method. 1 2 Science What is it that defines science? How is science distinguished from other academic endeavors (e.g, history or English)? Why is creationism or intelligent design not considered science by scientists? Science is about Observing 3 4

2 The imagination of nature is far, far greater than the imagination of man. For instance, how much more remarkable it is for us all to be stuck half of us upside down by a mysterious attraction to a spinning ball that has been swinging in space for billions of years, than to be carried on the back of an elephant supported on a tortoise swimming in a bottomless sea. Richard Feynman We live in a scientific age, yet we assume that knowledge of science is the prerogative of only a small number of human beings, isolated and priestlike in their laboratories. This is not true. Science is part of the reality of living; it is the what, the how and the why of everything in our experience. Rachel Carson (Silent Spring) 5 6 Evolution is a theory. It is also a fact. Facts and theories are not rungs in the hierarchy of increasing certainty. Facts are the world s data. Theories are the structures of ideas that explain and interpret facts. Facts do not go away while scientists debate theories to explain them. Einstein s theory of gravitation replaced Newton s, but apples did not suspend themselves in midair pending the outcome. Stephen Jay Gould da Vinci Study available literature Systematic observations Experimentation Careful repeated measurements Formulation of theoretical models Frequent attempts at mathematical generalizations 7 8

3 Scientific Method Our understanding of the world grows as our theories become more complete and precise. A key to science is the scientific method, in which the results of a good experiment can be reproduced. The same experiment using the same hardware will produce the same results time after time. If a hypothesis can not be tested then it falls outside the current realm of scientific understanding or knowledge, and is considered speculation. Scientific Method 1. Start with an educated guess or hypothesis or a question. 2. The guess could lead to a prediction that can be tested. 3. Design an experiment to test the hypothesis and prediction. 4. Evaluate the results of the experiment (e.g., the observations) to verify or refute hypothesis. 5. Construct a theory (or model) based on experiment results. 6. Repeat cycle (1-5) to refine/modify the theory "No amount of experimentation can ever prove me right; a single experiment can prove me wrong." Einstein Meteorologists use scientific principles to observe, understand, explain, or forecast the atmosphere s behavior. It is a characteristic of science that no theory is ever considered certain

4 Fields in Meteorology Fields in meteorology include Agricultural and forest meteorology Atmospheric chemistry Aviation/navigation weather Biometeorology Climate Dynamic meteorology Global climate change Instrument development Mesoscale meteorology Micrometeorology Paleoclimatology Tropical meteorology Extra-terrestrial atmospheres Meteorology Jobs Weather Forecaster Forensic meteorologist Air-quality meteorologist Research in all the sub-fields Teaching, Etc Meteorology Employment Federal Government NOAA (NWS), EPA, NASA, DoE, FAA, etc. Military Air Force, Navy, Army, etc. Civilian Airlines, Investment firms, Instrument makers, Law Firms, Utilities, Agriculture, Forecasting Accuweather, TV Stations, etc Meteorology at the University of Hawaii? My Specialty is Bad Weather There are 13 faculty and about 60 students in the UH Met department We each have research specialties Climate change Weather prediction Pollution dispersion Extra terrestrial weather Etc

5 My Specialty is Bad Weather Detecting Lightning with a Radio Hazardous Weather Causes Loss of Life and $Billions in Damage to Property and Lost Crops. Goal: To find new ways to observe and model our atmosphere to better understand and predict the storms that cause the weather hazards. Very Low Frequency noise generated by lightning travels very long distances through the atmosphere Detecting Lightning with a Radio This noise can be detected by a network of special receivers located on remote Pacific islands. Studying Hurricanes Water the Engine that Fuels Storms 19 20

6 Studying Hurricanes Developing a Hurricane Balloon We know hurricanes gain their energy (water vapor) from the ocean, but we are not exactly sure how they do this. Airplane pilots will not fly through hurricanes near the ocean surface. So how do we make the critical measurements that we need? Developing a Hurricane Balloon Radiation Imbalance and Creation of Jet Stream Release in Hawaii The distribution of sunlight available to heat the earth depends on 1.Geometry 2.Reflection/Albedo 3.Differing atmospheric path lengths 4.Season (tilt of Earth s axis of rotation relative to incoming sunlight) 23 24

7 Radiation Budget at the top of the Earth s Atmosphere Geometry Summer Fall Winter Red Line is incoming radiation from the sun Blue Line is outgoing radiation emitted by the earth Geometry Path Length through Atmosphere Path lengths for sun light through the atmosphere are longer at higher latitudes than at lower latitudes. The same amount of sun light is spread over a larger area at higher latitudes. Therefore, more sunlight is absorbed and scattered away at higher latitudes

8 Impact of Reflection (Albedo) Distribution of Reflectivity There are more clouds and ice at higher latitudes to reflect more sunlight (i.e., higher albedo). Reflected sunlight is not available to heat the earth Distribution of Reflectivity Radiation Imbalance 1. Geometry 2. Reflection/Albedo 3. Differing atmospheric path lengths The factors that cause the seasons also lead to a local radiation imbalance whereby Incoming > outgoing at low latitudes Incoming < outgoing at high latitudes 31 32

9 Radiation Imbalance A Balancing Act The difference between the absorbed sun light and the emitted outgoing long wave radiation of the Earth is referred to as the net radiation budget. Global-scale circulations in the atmosphere and currents in the oceans redistribute the excess energy, moving the energy from the lower latitudes to the poles to compensate for the radiation imbalance A Balancing Act A Balancing Act Europe's heating system. This highly simplified cartoon of Atlantic currents shows warmer surface currents (red) and cold north Atlantic Deep Water (blue). SST image shows Gulf Stream passing near the North Carolina Coast 35 36

10 Ocean Currents Atmospheric Circulation The general circulation of the atmosphere accounts for the rest of the heat transport needed to balance the radiational forcing. Ocean currents account for roughly 20% of the thermal advection needed to balance the radiation forcing A Balancing Act Seasonal Surface Temperature Variation A schematic of the Earth s weather machine bringing warm moist air northward and cold dry air southward (advecting latent and sensible heat)

11 Polar Jet Stream and the Thermal Wind 500 mb Height Field The jet stream associated with the polar front owes it existence to the differential solar heating from equator to pole. Thus, the jet is stronger in winter than in summer and moves north and south with the sun. Note the zonal or east-west orientation of the heights and the slope (gradient) of the pressure surface on both sides of the equator, which is concentrated in middle latitudes Explaining the Slope 0 mb 200 mb 400 mb 600 mb Imagine the atmosphere is a block of fluid that pushes down with 1000 mb of pressure at the bottom The block starts out at a uniform temperature the thickness of the atmosphere is the same everywhere. Now we make the block cold on the north side and warm on the south side Thickness 0 mb 200 mb 400 mb 600 mb The 1000 mb pressure surface is still flat there is the same amount of fluid above the surface whether you are on the cold side or the warm side But at upper levels, a pressure gradient appears L 800 mb 800 mb COLD WARM 1000 mb North South 1000 mb Y 43 X H 44

12 Thickness 0 mb The 1000 mb pressure surface is still flat there is the same amount of fluid above the surface whether you are on the cold side or the warm side Thickness 0 mb The 1000 mb pressure surface is still flat there is the same amount of fluid above the surface whether you are on the cold side or the warm side 200 mb But at upper levels, a pressure gradient appears Which gets stronger as you go up. 200 mb But at upper levels, a pressure gradient appears Which gets stronger as you go up. 400 mb L 400 mb L 600 mb 600 mb 800 mb 800 mb North South 1000 mb Y North South 1000 mb Y X H 45 X H 46 Thickness 0 mb The 1000 mb pressure surface is still flat there is the same amount of fluid above the surface whether you are on the cold side or the warm side Thermal Wind 200 mb But at upper levels, a pressure gradient appears Which gets stronger as you go up. 400 mb L 600 mb 800 mb North South 1000 mb Y X H 47 The thermal wind is the change or shear in the geostrophic wind with height under conditions of hydrostatic balance. 48

13 Deriving the Thermal Wind Relationship mb Thickness with 700mb Winds If we differentiate the geostrophic wind, (where f is the Coriolis parameter, k is the vertical unit vector, and the subscript "p" on the gradient operator denotes gradient on a constant pressure surface) with respect to pressure, and integrate from pressure level from p0 to p1, we obtain the thermal wind equation: Most of the gradient in thickness is concentrated in a narrow band in the middle latitudes. in winter.. Substituting the hypsometric equation, one gets a form based on temperature, = Thickness in meters between the heights of the 1000 and 500 mb levels Jet Streams Jet Streams The average position of the polar jet stream follows the sun, south in winter, north in summer. And it is much weaker in summer

14 Economic Considerations Questions? Jet Streams provide energy used in winter storms to produce high impact weather. Jet streams provide steering for high impact winter storms tracks. Aviation Interests need to predict jet streams to improve fuel efficiency and avoid clear air turbulence. The influence of the Rocky Mountains on the location of the jet stream over the Atlantic is a large part of why Europe enjoys warmer air currents than their latitude would warrant. Others? 53 54